i was wondering what the diff between the ecu for a pre/ post 85.5 . i know that the chip is removeable in the post but do the harnesses match, are their anny othe diffs, like settings. my 84 has a 2.7 out of what i have no idea but it still only is an 8v. just wondering if i should keep the ecu or swap it w/ the one from the 85.5(it is an auto) are their anny other parts worth swapping?????

You need to change both the DME and AFM. The early DME sends an 8 volt reference signal to the AFM, and the late DME sends a 5 volt reference. If you swap just the DME, the signals coming from the early AFM will be WAY off.

With the exception of the idle stabilizer circuit, the wire harness is the same, so this is a "plug and play" swap. I've done this to my '84 and it works great.

Cliff,
If I understand what you're saying, you installed a late model DME and a late model AFM into your '84 using the existing wiring? Any idea what the differences are (electrically) between the late AFMs and the 968 hot wire version? Thanks

Yes, you can swap in late model parts and use the existing DME harness.

I haven't delved into the 968 electronics, but from a strictly electronic stand point an AFM is an apple, and a hot wire MAF is an orange.

The AFM uses a flapper and spring pressure to measure air flow. As the flapper moves a wiper moves across a calibrated resistance and sends a signal to the DME.

With a hot wire MAF, incoming air cools the heated element, which unblances a precision resitor bridge. The unbalanced bridge then sends a signal to the DME.

The difficult part is converting the output from the hot wire MAF to a signal that the DME can use. There are aftermarket "kits" (AutoThority and Hutley Racing) that can do this, but they are WAY expensive (over $1K).

You don't need the idle stabilizer. If you really want to use it you need to add two wires and a 2 pin connector to the early DME harness. The hard part is finding the correct style of pins for the plugs.

Save youself some aggravation and don't worry about using the idle stabilizer.

__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!

Both idle control valves or bypass valves or possitioners or what ever your favorite schematic or parts lists calls them, use 12 volts off of the DME relay.

The early 944's use the fuel pump power and the later use the power to the injectors. Both come off the DME relay and not the DME.

Pins 33 and 34 at the DME connector are what go to the later idle possitioner. These are not in the loom for the early DME's. The DME pulses these to ground to shift and hold the valve opening.

The early idle regulator uses power from the fuel pump power circuit through a heated element to force a bi-metalic spring to close the blade valve. This is a set timed system.

As far as I can tell you can put a later DME into an early car but you have to replace the early AFS with the latter AFS because of the change is resistence curves and the lower control voltage.

You have to keep the early idle control valve.

__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!

the only thing wrong is the chip isn't removeable and the car had several water leeks.i would immagine porsche changed the dme for a better version. my lower block is out of a post 85.5 car annyway. it has the updated guide, ect but it is from the factery, they changed the roller and added the guide around 87 i think. either way i just finished rebuilding the engine and would rather do everything i can now . i am getting rid of the 85.5 and just want to make sure i have everything i can possible use to swap to the 84. parts an'r cheep, as i amsure you are aware.i just want everything i can swap and keep as many spare parts as posssible. i am moveing from chas.sc to houston tx and don.t want to drag my parts car with me. it is a lot cheeper to replace the chip than purchase a new dme. another quest. some 944's didn't come with ac, can i just rip out the ac system and get a belt for a car that didn't have one? als can you swap the alternaters? is the underdrive pully worth it? i am keeping the car registered in sc(i am going to school in texas) and we don't have inspection here. i just want to take care of everything now esp before i drive it to texas.

You can delete the A/C compressor by replacing the mounting bracket and getting a different drive belt, but if you're moving to Huston you'll need A/C. I have family in the Huston area, I spent the summer of '98 in Dallas/Ft. Worth, and Texas is HOT, HOT, HOT!

I was stationed in Charleston back in the early '70's, and I currently live 'just up the road' in Charlotte NC, so I know about East Coast weather. Trust me on this, you want A/C if you're moving to Texas.

As for an underdrive pully, forget it. Turning the alternator at a lower speed forces the voltage regulator to "max out" and shortens is life span.

Look at it this way: An alternator is designed to operate within a certain RPM range. The amount of current generated is a function of the voltage applied to the armature windings and the speed of the rotating magnetic field. If the regulator is maxed out, and the RPM is low, the alternator cannot develope its rated output. Since the early alternators are under-rated to start with (only 90 amps max), running the car for an extended time in this condition will do more harm than good.

What I would recommend is making sure that the engine coolant, electrical, and A/C systems are running properly.

As for swapping parts, you MAY be able to swap out the alternator bracket and then use the 85.5 alternator and A/C compressor. If this works out you get an additional 20 amps of current.

thanks for the input. i moved here from fla and never used my ac. in every other car i have ever owned that was the first thing to go. didn't some 944's come w/out ac??? if so did they have a different size pully on the alt.

Early 944's have a five rib belt; later have a six rib belt. Reason being the later cars have a larger alternator -- more amps. So you have to replace the drive pulley on the crank. The one with the four small bolts.

I understand your desire to optomize your resoruces and part out the 85.5. But there is really no performance differences between the early and later DME's. True some of the later DME's had a socketed CPU but you can buy a socket and put one in the early DME's. I suggest FRWilk's add on where there are two programs you can switch between to pass smog.

You may be able to use the AC compressor and condensor from the 85.5 but not the evaporator and blower. Different dash design.

I would take the front seats out of the 85.5 and the rear hatch. Strip out the doors and take the side mirrors, switches, glass, window drives and door handles. You might check to see if the gaskets on the doors and around the door opening are better that the 84 and transfer these as necessary.

Also take the speakers out of the 85.5. Remove the quarter windows and the side trim to get to the rear speakers.

The front struts are the same between the two cars. The aluminum a-arms are not. Stick with the steel as the ball joints are easy to replace.

The axles for the auto are a different lenght than the stick but the CV joints are the same. Pull the axles and tale the CV joints. Also pull the rear discs off and take the e-brake shoes and hardware. These shoes are over $60 if you have to buy them.

The wiper motor and the headlight motor are good to have as spares too. Pull all the relays out of the fuse/relay box and save them. Put the DME relay in your 84's glove box.

Pull the rear tail lights. If you get rear ended these will come in handy.

take the radiator and fans also. The six balded fans are far more efficent than the early three bladed units. Cut off the wires for the fans so you can splice them into your wires.

There is one difference between the early and later engines; the exhaust cam timing/duration is longer on the later engines. So use the later cam.

What shape is the 85.5 body in?

__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!

the dme on the 85.5 has been chipped,the seats are power(heavier)i don't want either ac. the back hatch in the 85.5 is HORRIBLY sunspotted and has the wiper(more weight) and i am working on a flat carbon fiber rear decklidw/ a virticle window.i have allready replaced the balljoints in the a arms i allready did the brakes(tons of fun) their are no speakers in the.5 the headlights are fixed on the 84 i have 2 extra dme reayys not includeing the one in either car.the tail lights are crap on that car, the pass lense is broken and the drivers is cracked. i allready swaped the fans but not the radiater, isnt the capacity of the auto smaller because of the trans cooler lines?i used the cam when i rebuilt the top half of the engine(snapped belt.i also swapped the injectors. i am deffinatly keeping the old ex manifold, i had to replace the manifold in the .5 twice before i went with the old style. the cv joints and axles where replaced 6 months ago.the body on the .5 is good. the pass side was sideswiped(bareley and the nose pannel is gone(i rearended a guy w/ no brakelights and never got around to replaceing it.it also has the turbo/s2 front end(missing the driveing lights.